So i'm filling up my tank yesterday, and I see another guy with an M3 also filling up at the pump next to me. I couldnt help but notice he was putting 87 octane in his car (I always use 91). So I asked him why he uses 87. He said that he "used to use 91 and since he switched he cant tell any difference in performance, and it is top tier gas". Im wondering what if any affect the use of lower octane would have on the car long term. I dont intend to switch, no way in hell.

It was Chevron. He didnt look cheap. I fact he looked friggin rich! And 91 is the highest we can get in LV.

He is cheap, and stupid. What reason other than money would someone ever get 87 over 91 or 93 or 94? Seriously, this is an ///M we are talking about. If someone doesn't like putting high-test, or wide expensive tires or expensive breaks on their car, why on earth did they buy an ///M.....just get a 328, or 335 or 335d (the best) and enjoy those GREAT cars. Again, if you need to go off-roading or haul lumber you don't buy a civic or F430. Different cars, different focuses, different purposes......its not rocket science.

It was Chevron. He didnt look cheap. I fact he looked friggin rich! And 91 is the highest we can get in LV.

BTW, how does somebody look rich? You can never really tell. Those are often the people who are broke because they spend all of their money on trying to look "rich," with nothing left to back it up. No baller is going to be pinching pennies at the pump... (PP@P)

Octane rating does not relate to the energy content of the fuel. It is only a measure of the fuel's tendency to burn in a controlled manner, rather than exploding in an uncontrolled manner. Where the octane number is raised by blending in ethanol, energy content per volume is reduced.

87 octane has more energy in it than 91.

As long as his engine is not pinging -- no harm done really.

and to the person that mentioned "LED" (sic) --- there hasn't been any lead in pump gas for years and years

Sounds like a cheap bastard who needs a swift kick in the nuts! My ex's parents used to put 87 in their E46 325i when they first got it. Then they wondered why they kept having so many engine issues... Then their warranty was stripped once the service department tested their gasoline. I used to get so mad at them for it, too. Her dad and I argued quite a bit about it, hahaha.

Since he's rich, gas won't be a factor for him. Anyways, why would someone do that? ///M3's are meant for high performance and should use 91 oct out of the factory, unless it's modified to use race gas, etc. That's another story.

BMW recommends 93 octane with a minimum fuel grade of 91. They further state "Do not use any gasoline below the specified minimum fuel grade. Otherwise the engine could be damaged.".

Implied here - if the engine is damaged due to low grade (i.e.: 87 octane) fuel, repairs under warrenty may not be covered! With the price difference between 87 and 91/93 you'd have to fill up an awful lot to pay for an new engine!

BMW recommends 93 octane with a minimum fuel grade of 91. They further state "Do not use any gasoline below the specified minimum fuel grade. Otherwise the engine could be damaged.".

Implied here - if the engine is damaged due to low grade (i.e.: 87 octane) fuel, repairs under warrenty may not be covered! With the price difference between 87 and 91/93 you'd have to fill up an awful lot to pay for an new engine!

Just curious...to all of you here who live in 91 octane land, do you really think you are getting the full rated power of this engine? My bet is that you are not. 93 or even 94 octane and cold, dry air at sea level is likely needed for a highly tuned, high revving motor such as this to achieve it's stated power output. I don't know for sure on the M3, but this was definitely the case when I had my RS4.